1. Field of the Invention
The present invention relates to a feed device for a sewing machine. The feeding device related to the invention incorporates an upper feed dog which executes fabric-feeding operations above a throat plate in association with a lower feed dog installed below the throat plate to enable the upper and lower feed dogs to properly deliver feeding force onto and below material fabrics so that material fabrics can smoothly be delivered to a needle drop point. In particular, the invention relates to the upper feed dog provided for the feed device.
2. Description of the Related Art
Conventionally, delivery of material fabrics is executed by exerting feeding force to material fabrics inserted between a presser foot provided for a sewing machine extending to the front and the back of the needle drop point and a throat plate provided for a bed, by the use of a lower feed dog installed below the throat plate. Using a conventional feed device, the lower feed dog performs predetermined feeding operations in association with the operation of the sewing machine. Concretely, the lower feed dog performs elliptic movement in substantially vertical surface along the feeding direction. The lower feed dog projects itself above the throat plate at the upper domain of the locus of the elliptic movement. Simultaneous with the projecting movement of the lower feed dog, material fabrics are sandwiched between the lower feed dog and the bottom surface of the presser foot.
Nevertheless, when operating the conventional feed device cited above, the lower feed dog exerts its feed force only to the bottom of material fabrics. In consequence, when, for example, plural material fabrics are sewn together, a gap is easily generated between the bottom fabric receiving the feed force and the top fabric slipping itself along the presser foot. Therefore, in order to securely yield quality goods from a sewing operation without incurring sewing slippage at all, operator of any conventional sewing machine needs to manually perform delicate adjustment of fabric feeding mechanism in front of the feed device.
When operating any of above mentioned sewing machines like an interlock chainstitch sewing machine, or a one-needle double chainstitch sewing machine, or a multi-needle double chainstitch sewing machine for example, in addition to a proper lower feed dog provided below the throat plate, an upper feed apparatus may be provided. The upper feed apparatus is of such a structure having an upper feed dog which is disposed above the throat plate in front of the needle drop point in order that fabric-feeding operation identical to that is performed by the lower feed dog can be executed in association with this lower feed dog. Material fabric transferred onto the throat plate is sandwiched between the upper and lower feed dogs before affecting feed force to the top and bottom surfaces of the sandwiched fabric.
Concretely, the conventional upper feed apparatus has an operating rod which is set to a predetermined position close to the needle drop point by way of projecting itself in the downward direction from the interior of the sewing machine and a feed body which is secured to the tip domain of the operating rod. The upper feed dog is provided at an end of the feed body which extends itself to the front of the needle drop point by way of facing the top surface of the throat plate. The operating rod is connected to the drive unit of the sewing machine via predetermined transmission mechanism. The operating rod swings itself back and forth in the feeding direction simultaneously with its linear movement being performed in the vertical direction in association with mechanical operation of the sewing machine.
In correspondence with those movements performed by the operating rod, the upper feed dog executes elliptic movements in association with the mechanical operation of the sewing machine and in synchronization with the operation of the lower feed dog installed below the throat plate. While the upper feed dog moves downward, it closely approaches the lower feed dog which moves upward, and then, both the upper and lower feed dogs conjunctionally shift themselves to the rear domain of the feeding direction. As a result, a pair of material fabrics transferred onto the throat plate are tightly inserted between the upper and lower feed dogs before eventually being delivered to the needle drop point by effect of feed force transmitted from the upper and lower feed dogs, thus enabling sewing operators to solve those technical problems cited earlier.
When operating any conventional sewing machine incorporating such an upper feed apparatus based on the structure described above, in order to generate an adequate amount of feed force between the upper and lower feed dogs, fixing position of the feed body of the operating rod is variable. This in turn permits adjustment of clearance between the upper and lower feed dogs being close to each other. In other words, initial adjustment of the feed gap is performed for the material fabrics in proportion to the thickness of the inserted material fabrics before eventually starting off the sewing operation.
Nevertheless, when operating any of those conventional sewing machines requiring provision of the upper feed dog like an interlock chainstitch sewing machine or a one-needle double chainstitch sewing machine for example, in particular, when changing condition of double fabrics or folding condition of these material fabrics on the way of sewing operation, an operator often performs such an operation in order that the thickness of those material fabrics can continuously be varied or on the stepwise basis. In this case, when a sewing operation is executed against thicker domain of the material fabrics, these material fabrics are tightly inserted between the upper and lower feed dogs, thus easily incurring damage to the material fabrics. Conversely, when a sewing operation is executed against those relatively thin domains of those material fabrics, the upper feed dog remains inoperative to merely result in the insufficient feed force, thus unavoidable generating sewing slippage. In consequence, quality goods cannot securely be yielded from a sewing machine provided with the conventional feed device.